Thursday, April 2, 2009

Riding the Anchor

I've been tweaking my riding sail for a few days now, and I think I finally have it about right and in a place that doesnt' block the solar panels too much. I like it. I think my dragging episode a few days ago was primarily due to not having enough scope (anchor rode/chain) out, but also Sula tends to 'hunt' at the anchor, meaning that she will yaw back and forth and even sometimes present her broadside to the wind. This is due to the weathervane effect. She has too much windage forward, with the roller furling headstay and the mast both forward of the center. The riding sail counteracts those forward areas by providing a large surface area of windage aft that helps to make her a more effective weathervane, her bow always seeking the eye of the wind. It works pretty well. The constant yawing back and forth at the anchor tends to put much higher loads on the anchor and hence the mud, as you can imagine when she is swinging hard and presents her beam to the wind and the wind is really blowing it will put lots of strain on things down on the bottom. So much strain that with improper scope (maybe 3:1 like I had before) the anchor will steadily drag through the mud and the boat will end up on the rocks. Most riding sails are a single piece of sailcloth. This one was inspired by a German unmanned rocket tail design from the WWII era. In my mind the advantage is that it is providing a more constant drag, and when the angle of attack changes as the boat yaws, it more quickly gives a significant force to correct for the wind direction. A typical riding sail will need to yaw futher to provide much force. This riding sail does have the disadvantage of providing a fair amount of drag even with zero angle of attack, so in super high winds it would probably create lots of drag.

Anyway. What a beautiful day! It was 80 degrees out and low humidity. A light breeze. Just awesome. I went for a swim and didn't want to get out of the water it was so refreshing. As you can see in the pics, there was a slight haze in the air, that gave the mountains that awesome effect of seeming to stretch all the way into the sky.

I'm headed to Tucson tomorrow to pick up Sara from the airport. With two anchors down now with proper scope I'm sure things will be fine while I'm away. Warm spring breezes to all those up north!!